Development of polyhydroxybutyrate based blends for compostable packaging
2011-02-14T15:03:24Z (GMT) by
In this research, three polymers have been blended with polyhydroxybutyrate: poly(ethylene glycol), maize starch and polylactic acid. Their morphology, structure, thermal, rheological, mechanical properties and biodegradation behaviour have been studied. Blends of PHB and PEG, at three different concentrations (2, 5 and 10 wt %) were prepared by solvent-casting. For these blends the glass transition temperature and crystallization temperature decreased with increasing PEG content, while the addition of a low level of PEG (2% and 5%) did not change the thermal stability of the blends. Blends of PHB with maize starch (72% amylopectin), at different weight ratios of 100/0, 90/10, 80/20, 70/30, 60/40 and 50/50, respectively, were prepared by melt compounding. The physical properties were found to be optimum at a 70/30 ratio. Blends of PHB with two types of maize starch (28% amylose and 70% amylose) were prepared at a ratio of 70/30. The starch granules act as a filler and nucleating agent for PHB. Intermolecular hydrogen bonding was observed in the PHB/starch blends. Hydrogen bonding was found to be stronger between PHB and high amylose content starch. Thus the PHB/70% amylose starch blends showed greater improvement in thermal stability, melt viscosity and mechanical properties compared with the PHB/28% amylose starch blends. Blends of PHB and PLA at a number of different weight ratios (100/0, 75/25, 50/50, 25/75, 0/100) were prepared by melt compounding. The results indicate that PLA/PHB blends are immiscible but exhibit some molecular interaction. PHB is highly crystallisable and it enhances the recrystallization of PLA and results in an increase in the heat distortion temperature. Adding PLA to PHB improves the mechanical properties of PHB. In fact, blending with PHB is also a viable approach to improve the mechanical properties of PLA because the PLA/PHB 75/25 blend exhibits significantly improved tensile properties compared with pure PLA. This is due to the finely dispersed PHB crystals acting as a filler and nucleating agent in PLA. The biodegradability of the blends, studied by weight change measurement at room temperature, improved with increasing PHB content.